Method and apparatus for detecting the seam position of electric resistance welded steel pipes

Abstract

This invention provides a seam position detection method that can accurately detect the seam portion of electric resistance welded steel pipes in a manufacturing line for electric resistance welded steel pipes. [Solution] The process includes: step A, which is to image the vicinity of the seam irradiated with light from a light source on the downstream side of the line of the cutting position of the weld bead; step B, which is to detect the positions of both ends of the bead cutting portion from the brightness image of the vicinity of the seam irradiated with light from a light source; and step C, which is to identify the position of the seam portion based on the positions of both ends of the bead cutting portion detected in step B. In step B, the starting point for searching for the end position of the bead cutting portion with respect to the brightness image is set within the area of ​​the bead cutting portion, and the search is performed from the starting point toward both sides in the circumferential direction of the pipe, and the point where the brightness or the brightness difference between adjacent cells first exceeds a threshold is detected as the end position of the bead cutting portion.

Description

Technical Field

[0001] The present invention relates to a seam position detection method and apparatus for highly accurately detecting a seam portion after welding bead cutting for annealing the seam portion or the like in a production line of electric welded steel pipes.

Background Art

[0002] Generally, in a production line of electric welded steel pipes, after bending a steel strip into a tubular shape with a forming roll group, both ends of the steel strip are butted at the upper part and welded (butt welding). Thereafter, the welding bead formed on the welded portion is cut and removed, and further, annealing (seam heat treatment) for reheating the welded portion (seam portion) is performed to improve the material properties of the welded portion, thereby manufacturing an electric welded steel pipe.

[0003] Annealing of the seam portion (sometimes also called the welded seam portion) is often performed multiple times by induction heating. It is important to accurately align the heating device (annealer heater) with the seam portion and heat only the seam portion without affecting the base material. However, in the production line, since path line fluctuations and twists of the electric welded steel pipe occur, misalignment between the heating portion and the seam portion easily occurs. Therefore, at present, an operator sometimes visually observes the running state of the electric welded steel pipe and the misalignment between the seam portion and the heating portion, and manually performs position correction of the annealer heater as appropriate.

[0004] In annealing of the seam portion, it is ideal to heat so that the center of the heating range coincides with the seam portion. On the other hand, it is difficult to identify the seam portion by appearance. Therefore, usually, the bead cutting portion having increased gloss compared to the surrounding base material portion by cutting the welding bead is regarded as the seam portion, and an operator visually checks whether the position of the seam portion and the position of the heating portion, that is, the annealer heater, coincide, and conducts the operation.

[0005] However, in this case, accurately monitoring the seam area would require an operator to constantly monitor the positional relationship between the heating element by the annealer heater during manufacturing and the seam area, which would prevent them from engaging in other tasks. To solve this problem, various methods and devices for detecting the seam position of electric resistance welded steel pipes have been proposed. For example, Patent Documents 1 to 4 utilize the fact that the bead cutting portion of an electric resistance welded steel pipe and the base material portion have different mirror-like properties, and detect the bead cutting portion including the seam portion based on the reflected light brightness of an image captured by irradiating light near the seam portion. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-120985 [Patent Document 2] Japanese Patent Publication No. 2015-219124 [Patent Document 3] Patent No. 7151912 [Patent Document 4] Japanese Patent Application Publication No. 6-241740 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the surface of the base material near the seam contains roll marks and black scale patterns of the material, which act as brightness disturbances. For this reason, methods for obtaining the maximum and minimum brightness values ​​or brightness differences disclosed in Patent Documents 1 to 4, or methods for searching for areas exceeding a threshold from the edge of the image and detecting them as bead cutting areas, have the problem of misidentifying the brightness values ​​or brightness differences of reflected light generated on the base material of the electric resistance welded steel pipe due to the above disturbances as bead cutting edges, resulting in a deterioration of the accuracy of detecting the position coordinates of the seam.

[0008] Therefore, the object of the present invention is to solve the problems of the prior art described above and to provide a seam position detection method and apparatus that can accurately detect the seam portion of electric resistance welded steel pipes in an electric resistance welded steel pipe manufacturing line. [Means for solving the problem]

[0009] The inventors diligently studied to solve the above problems. As a result, they found that the above problems can be solved by setting the search starting point for the bead cutting section end position in a brightness image taken near the seam within the area of ​​the bead cutting section, performing a search from that starting point toward both sides in the circumferential direction of the pipe, and detecting the point where the brightness or brightness difference first exceeds a threshold as the "bead cutting section end position". This invention is based on the above findings and is summarized as follows.

[0010] [1] A method for detecting the seam portion of an electric resistance welded steel pipe in a manufacturing line for electric resistance welded steel pipes, The process (A) involves imaging the area near the seam where light is irradiated from a light source, downstream of the cutting position of the weld bead. Step (B) involves detecting the positions of both ends of the bead cutting portion from the brightness image of the seam area captured in step (A), The process includes a step (C) to determine the seam position based on the positions of both ends of the bead cutting portion detected in step (B), A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that, in step (B) above, the starting point for searching for the end position of the bead cutting portion with respect to the brightness image is set within the area of ​​the bead cutting portion, the search is performed from the starting point toward both sides in the circumferential direction of the pipe, and the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe) first exceeds a threshold is detected as the end position of the bead cutting portion.

[0011] [2] In the seam position detection method described in [1] above, the steps (A) to (C) for detecting the seam position are performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe. The method for detecting the seam position of an electric resistance welded steel pipe is characterized in that, in step (B), a search start point is set within the region of the bead cutting portion identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step. [3] In the seam position detection method described in [1] above, the seam position detection steps (A) to (C) are performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe. A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that, in step (B), the seam position identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step is set as the starting point for the search. [4] A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that, in any of the seam position detection methods of [1] to [3] above, step (C) identifies the center between the positions of both ends of the detected bead cutting portion as the seam portion position.

[0012] [5] A method for manufacturing electric resistance welded steel pipes in an electric resistance welded steel pipe manufacturing line, in which the seam portion of the electric resistance welded steel pipe is detected, The process (A) involves imaging the area near the seam where light is irradiated from a light source, downstream of the cutting position of the weld bead. Step (B) involves detecting the positions of both ends of the bead cutting portion from the brightness image of the seam area captured in step (A), The process includes a step (C) to determine the seam position based on the positions of both ends of the bead cutting portion detected in step (B), In step (B) above, the method for manufacturing electric resistance welded steel pipes is characterized in that the starting point for searching for the end position of the bead cutting portion with respect to the brightness image is set within the area of ​​the bead cutting portion, the search is performed from the starting point toward both sides in the circumferential direction of the pipe, and the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe) first exceeds a threshold is detected as the end position of the bead cutting portion.

[0013] [6] In the manufacturing method of [5] above, the steps (A) to (C) for detecting the position of the seam are performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe. The method for manufacturing electric resistance welded steel pipes, characterized in that, in step (B), a search start point is set within the region of the bead cutting portion identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step. [7] In the manufacturing method of [5] above, the steps (A) to (C) for detecting the position of the seam are performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe. The method for manufacturing electric resistance welded steel pipes is characterized in that, in step (B), the seam position identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step is set as the starting point for the search. [8] A method for manufacturing electric resistance welded steel pipes, characterized in that in any of the manufacturing methods described in [5] to [7] above, step (C) identifies the center between the positions of both ends of the detected bead cutting portion as the seam portion position.

[0014] [9] A device for detecting the seam portion of electric resistance welded steel pipes in a manufacturing line for electric resistance welded steel pipes, An imaging device (1) captures images of the area near the seam where light is irradiated from a light source, downstream of the cutting position of the weld bead. The imaging device (1) detects the positions of both ends of the bead cutting portion from the brightness image of the vicinity of the seam portion, and the image processing device (2) identifies the position of the seam portion based on the detected positions of both ends of the bead cutting portion. The image processing device (2) is characterized by setting a search starting point within the area of ​​the bead cutting portion when searching for the end position of the bead cutting portion with respect to the brightness image, performing a search from the search starting point toward both sides in the circumferential direction of the pipe, and detecting the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe) first exceeds a threshold as the end position of the bead cutting portion.

[0015]

[10] The seam position detection device described in [9] above, wherein the seam position detection step is performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe, wherein the imaging device (1) images the vicinity of the seam and the image processing device (2) detects the position of the seam based on the brightness image obtained from the imaging, The image processing device (2) stores the positions of both ends of the bead cutting part detected in the detection step one step before the current detection step, and sets a search start point within the area of the bead cutting part specified by the positions of both ends of the bead cutting part. A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that.

[11] In the seam position detection device of [9] above, the imaging device (1) images the vicinity of the seam part, and the image processing device (2) detects the seam part position based on the luminance image obtained by the imaging. A seam position detection device that periodically performs the detection step of the seam part position at a predetermined interval along the longitudinal direction of the electric resistance welded steel pipe, The image processing device (2) stores the seam part position specified by the positions of both ends of the bead cutting part detected in the detection step one step before the current detection step, and sets the seam part position as the search start point. A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that.

[12] In the seam position detection device according to any one of [9] to

[11] above, the image processing device (2) specifies the center between the positions of both ends of the detected bead cutting part as the seam part position. A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that.

Advantages of the Invention

[0016] According to the present invention, in the manufacturing line of electric resistance welded steel pipes, even when the seam part position is displaced in the circumferential direction of the pipe due to twisting or pass line variation of the electric resistance welded steel pipe, it is not affected by roll marks, black skin patterns, etc. present in the steel pipe base material part, and the bead cutting part can be accurately detected and the seam part position can be specified (detected).

Brief Description of the Drawings

[0017] [Figure 1] An explanatory diagram schematically showing a part of the manufacturing line of an electric resistance welded steel pipe and an embodiment of the device used for implementing the seam position detection method of the present invention [Figure 2] A drawing showing the luminance distribution in the circumferential direction of the pipe obtained from the captured image near the seam part of the electric resistance welded steel pipe [Figure 3]This diagram shows the absolute value distribution of brightness difference in the circumferential direction of the pipe (brightness difference between adjacent cells in the circumferential direction of the pipe) obtained from images taken near the seam of an electric resistance welded steel pipe. [Figure 4] This diagram shows the absolute value distribution of brightness difference in the circumferential direction of the pipe (brightness difference between adjacent cells in the circumferential direction of the pipe) including disturbances in the base material, obtained from images taken near the seam of an electric resistance welded steel pipe, as well as the starting point (position) of the search in the present invention and the end position of the bead cutting portion detected by the search. [Figure 5] Figure 5(a) is an image of the vicinity of the seam of an electric resistance welded steel pipe in an embodiment, which showed false detection with the conventional method but good detection with the present invention method. Figure 5(b) is a diagram showing the absolute value distribution of brightness difference in the circumferential direction of the pipe (brightness difference between adjacent cells in the circumferential direction of the pipe), obtained from the X-X' cross section of the image in Figure 5(a). [Modes for carrying out the invention]

[0018] The present invention provides a method for detecting the seam portion of an electric resistance welded steel pipe in an electric resistance welded steel pipe manufacturing line. The method comprises the steps of: (A) imaging the vicinity of the seam portion illuminated by light from a light source using an imaging device downstream of the welding bead cutting position (welding bead cutting machine); (B) detecting the positions of both ends of the bead cutting portion from the brightness image of the vicinity of the seam portion captured in step (A); and (C) identifying the seam portion position based on the positions of both ends of the bead cutting portion detected in step (B). The " vicinity of the seam portion" imaged in step (A) refers to the seam portion and its vicinity (periphery), and is a region that includes at least the bead cutting portion, as will be described later.

[0019] In step (B) above, the end position of the bead cutting area is searched for in the brightness image. The "search start point" (search start position) is set within the area of ​​the bead cutting area, and the search is performed from that search start point toward both sides in the circumferential direction of the pipe. In this search, the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe; the same applies hereinafter) first exceeds the threshold (i.e., the first point where the threshold is exceeded that is searched) is detected as the "end position of the bead cutting area". In this invention, "exceeding the threshold" means either "exceeding the upper limit threshold" or "falling below the lower limit threshold." Specific embodiments include, for example, (i) luminance exceeding the upper limit threshold, (ii) luminance falling below the lower limit threshold, and (iii) luminance difference (absolute value) exceeding the upper limit threshold.

[0020] As mentioned earlier, there is a difference in mirror-like surface quality between the bead-cut area and the base material of electric resistance welded steel pipes. The bead-cut area can be detected by illuminating the vicinity of the seam with light and searching the brightness image in the circumferential direction of the pipe. However, the surface of the base material near the seam has roll marks and black scale patterns, which can cause significant changes in brightness even within the base material area. Therefore, if the search for areas where brightness or brightness difference exceeds a threshold is started from the edge of the image, the brightness change within that base material area may be mistakenly detected as the bead-cut area. In contrast, the bead-cut area has a smooth, mirror-like surface, and in normal manufacturing, it is imaged immediately after bead cutting, so the brightness hardly changes within the bead-cut area. Therefore, by setting the "search start point" within the bead-cut area, as in the present invention, and performing the search from this "search start point" toward both sides in the circumferential direction of the pipe, and detecting the point where brightness or brightness difference first exceeds the threshold as the edge position of the bead-cut area, the above-mentioned misdetection of the bead-cut area can be eliminated.

[0021] Here, the method of setting the search starting point within the bead cutting area is arbitrary, but in the present invention, the seam position detection steps (A) to (C) described above are performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe. Therefore, it is preferable to set the search starting point within the area of ​​the bead cutting area specified by the positions of both ends of the bead cutting area detected in the detection step immediately preceding the detection step (the detection step being performed; the same applies hereinafter). If the interval between seam position detection steps (imaging interval) is not too long, the amount of variation in the twist of the electric resistance welded steel pipe and the amount of variation in the bead cutting width between detection steps are sufficiently small. For this reason, the area of ​​the bead cutting area specified by the positions of both ends of the bead cutting area detected in the detection step immediately preceding the detection step is considered to roughly coincide with the area of ​​the bead cutting area in the detection step.

[0022] Furthermore, it is particularly preferable to use the "seam position" identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step as the search starting point, which allows for a more reliable setting of the search starting point within the bead cutting portion area. As will be described later, in each detection step for the seam position, the "seam position" can be set to the midpoint between the detected positions of both ends of the bead cutting portion. Therefore, the "seam position" identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step is considered to be within the bead cutting portion area of ​​that detection step with a fairly high probability.

[0023] Furthermore, the seam position detection device of the present invention is a device used to implement the method of the present invention described above, and therefore has the following configuration. That is, it is a device for detecting the seam portion of an electric resistance welded steel pipe in a manufacturing line for electric resistance welded steel pipes, and comprises an imaging device 1 that images the vicinity of the seam portion irradiated with light from a light source, downstream of the welding bead cutting position (welding bead cutting machine) in the line, and an image processing device 2 that detects the positions of both ends of the bead cutting portion from the brightness image of the vicinity of the seam portion captured by the imaging device 1, and identifies the seam portion position based on the detected positions of both ends of the bead cutting portion. The image processing device 2 sets a "search start point" within the area of ​​the bead cutting portion when searching for the end position of the bead cutting portion with respect to the brightness image, and searches toward both sides in the circumferential direction of the pipe from that search start point, and detects the point where the brightness or brightness difference first exceeds a threshold (i.e., the first point that exceeds the threshold) as the "end position of the bead cutting portion".

[0024] Here, for reasons similar to those for the seam position detection method of the present invention described above, the seam position detection device of the present invention is a seam position detection device that periodically performs a seam position detection step at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe, in which the imaging device 1 images the vicinity of the seam and the image processing device 2 detects the seam position based on the brightness image obtained from this imaging, wherein the image processing device 2 preferably stores the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step, and sets a search start point within the area of ​​the bead cutting portion specified by these positions of both ends of the bead cutting portion. Furthermore, it is particularly preferable that the image processing device 2 stores the "seam position" specified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step, and sets this "seam position" as the search start point.

[0025] Hereinafter, embodiments of the method and apparatus for detecting the seam position of electric resistance welded steel pipes according to the present invention will be described with reference to the drawings. Figure 1 schematically shows a part of the manufacturing line for electric resistance welded steel pipes and one embodiment of the apparatus used to implement the present invention. The manufacturing line shows the following steps: The left and right ends of the steel strip, which has been bent into a tubular shape by a group of forming rolls (not shown), are brought together by a squeeze roll 11 and then butt-welded using a welding device (not shown) to form an electric resistance welded steel pipe 10. After the weld bead is cut off using a welding bead cutting machine 12, the pipe is subjected to seam heat treatment (annealing) using a seam heat treatment equipment 13. The butt-welded electric resistance welded steel pipe 10 has a seam formed by the welding, and a weld bead, which is molten steel discharged to the surface, is formed in this seam. The weld bead cutting machine 12 cuts off the weld bead. Subsequently, the seam heat treatment equipment 13 performs seam heat treatment (annealing) to improve the material properties of the seam.

[0026] As a seam position detection device used in the implementation of the present invention, a light source 3 that irradiates light near the seam portion of the electric resistance welded steel pipe 10 and an imaging device 1 that captures the reflected light from the surface of the steel pipe from directly above are arranged downstream of the welding bead cutting machine 12. Furthermore, this seam position detection device includes an image processing device 2 that performs seam position detection processing based on the image captured by the imaging device 1. Light source 3 irradiates light near the seam after bead cutting. In the electric resistance welded steel pipe manufacturing line, the temperature of the steel pipe surface reaches a maximum of approximately 1100°C due to heat treatment in the seam heat treatment equipment 13. Therefore, it is preferable that the light emitted by light source 3 is in the wavelength range of 550 nm or less, which is less affected by the radiant light from the heated area on the steel pipe surface. Furthermore, a control unit (not shown) that controls the light intensity is connected to the light source 3. For example, if the distance from the light source 3 to the electric resistance welded steel pipe 10 changes due to a change in the diameter of the electric resistance welded steel pipe 10, the control unit will change the light intensity of the light source 3 according to the distance from the light source 3 to the electric resistance welded steel pipe 10.

[0027] The imaging device 1 images the area near the seam illuminated by light from the light source 3 (step (A) above). Typically, in the present invention, the seam position detection step is performed periodically at predetermined intervals (for example, at intervals of several hundred mm in the length direction of the steel pipe) along the longitudinal direction of the electric resistance welded steel pipe 10. Therefore, the imaging device 1 periodically images the reflected light reflected from the surface of the electric resistance welded steel pipe 10 (near the seam) as it moves along the manufacturing line, at predetermined intervals. The positional relationship between the imaging device 1 and the light source 3 may be either specular reflection or diffuse reflection. Here, the "near the seam" to be imaged refers to the seam and its vicinity (periphery), since the method of the present invention aims to detect the end position of the bead cutting portion. This region includes at least the bead cutting portion, and may be a wider region. However, if the imaging area is too wide, the area not used for actual measurement increases, and since the number of elements in the camera is finite, the resolution per pixel decreases. Therefore, it is best to choose an area of ​​appropriate size. Furthermore, the imaging device 1 has channels capable of receiving light in the wavelength range irradiated by the light source 3.

[0028] The imaging device 1 is connected to a control unit (not shown) that controls the focal length of the camera. For example, if the distance from the imaging device 1 to the electric resistance welded steel pipe 10 changes due to a change in the diameter of the electric resistance welded steel pipe 10, the control unit changes the focal length of the imaging device 1 according to the distance from the imaging device 1 to the electric resistance welded steel pipe 10. The method for changing the focal length of the imaging device 1 is not particularly limited; for example, the imaging device 1 can have a position adjustment mechanism to keep the distance between the imaging device 1 and the electric resistance welded steel pipe 10 constant.

[0029] The image processing device 2 is implemented, for example, by a general-purpose computer such as a workstation or personal computer. This image processing device 2 applies well-known image processing techniques to the image captured by the imaging device 1 to detect the position of the bead cutting portion, and further identifies the position of the seam portion based on this detection. The image processing device 2 includes a detection unit 4 that performs the steps of detecting the "positions of both ends of the bead cutting portion" from a brightness image of the vicinity of the seam portion captured by the imaging device 1 (step (B)), and identifying the "seam portion position" based on the positions of both ends of the bead cutting portion detected in step (step (C)), and a storage unit 5 that stores the detected and identified position data.

[0030] In the detection unit 4 of the image processing device 2, the process of detecting the positions of both ends of the bead cutting portion (step (B)) and the process of identifying the position of the seam portion based on the detected positions of both ends of the bead cutting portion (step (C)) are performed, for example, as follows. The bead-cut portion of the electric resistance welded steel pipe 10 has a higher specular surface compared to the uncut base material portion, and most of the irradiated light is specularly reflected. Therefore, in the brightness image obtained by the imaging device 1 under diffuse reflection conditions from the reflected light from the light source 3, the area corresponding to the bead-cut portion appears darker (lower brightness value) than the surrounding base material portion. Consequently, in the case of such a brightness image, the end position of the bead-cut portion (hereinafter referred to as the "bead-cut end position" for convenience of explanation) can be detected as follows. For example, the bead-cut end position can be detected by searching for a portion in the circumferential brightness distribution obtained from the brightness image near the seam portion shown in Figure 2, where the brightness value falls below a preset threshold. Alternatively, the bead-cut end position can be detected by searching for a portion in the circumferential brightness difference distribution obtained from the brightness image near the seam portion shown in Figure 3, where the brightness difference (absolute value) exceeds a preset threshold.

[0031] On the other hand, in the luminance image obtained by the imaging device 1 when reflected light from the light source 3 is captured under specular reflection conditions, the region corresponding to the bead cutting area appears brighter (higher luminance value) than the surrounding base material, in contrast to the case when diffuse reflected light is captured. Therefore, in general, in the case of such a luminance image, the position of the bead cutting end can be detected as follows. For example, the position of the bead cutting end can be detected by searching for a portion in the luminance distribution in the circumferential direction of the pipe obtained from the luminance image near the seam where the luminance value exceeds a preset threshold. Alternatively, as in the case of Figure 3 above, the position of the bead cutting end can be detected by searching for a portion in the luminance difference distribution in the circumferential direction of the pipe obtained from the luminance image near the seam where the luminance difference (absolute value) exceeds a preset threshold.

[0032] However, the surface of the base material outside the bead cutting area may have roll marks or black scale patterns, so the brightness can change significantly even within the base material area, as shown in the brightness difference distribution obtained from the brightness image near the seam area in Figure 4. In this case, if the search for areas where the brightness difference exceeds the threshold is started from the edge of the image, a change in brightness within the base material area will be detected at the initial stage, and this will be mistakenly identified as the bead cutting edge. On the other hand, since the bead cutting area is a smooth mirror surface, the brightness hardly changes within the region of the bead cutting area. Therefore, in the present invention, for example, in detecting the position of the bead cutting end using the brightness difference distribution, in order to avoid mistakenly detecting brightness changes due to roll marks or black scale patterns on the base material as the bead cutting end, a "search start point" is set within the region of the bead cutting area as shown in Figure 4, and a search is performed from this search start point toward both sides in the circumferential direction of the pipe, and the points where the brightness difference (absolute value) first exceeds the threshold, i.e., points where the brightness difference (absolute value) exceeds the threshold, are detected as bead cutting end positions a and b, respectively.

[0033] The present invention, which involves setting the "search starting point" within the area of ​​the bead cutting section and performing the search in this manner, can of course also be implemented in the following embodiments. (i) For the luminance distribution in the circumferential direction of the pipe obtained from the luminance image near the seam as shown in Figure 2, the "search start point" is set within the area of ​​the bead cutting section, and a search is performed from this search start point toward both sides in the circumferential direction of the pipe, and the point where the luminance first exceeds the threshold, i.e., the point where the luminance first exceeds the threshold, is detected as bead cutting end positions a and b, respectively. (ii) When the reflected light from the light source 3 is captured by the imaging device 1 under specular reflection conditions, the "search start point" is set within the area of ​​the bead cutting portion for the luminance distribution in the circumferential direction of the pipe obtained from the luminance image near the seam portion, and a search is performed from this search start point toward both sides in the circumferential direction of the pipe, and the point where the luminance first exceeds the threshold, i.e., the point where the luminance first falls below the threshold, is detected as the bead cutting end positions a and b, respectively. (iii) When the reflected light from the light source 3 is captured by the imaging device 1 under specular reflection conditions, the "search start point" is set within the area of ​​the bead cutting portion for the luminance difference distribution in the circumferential direction of the pipe obtained from the luminance image near the seam portion, and a search is performed from this search start point toward both sides in the circumferential direction of the pipe, and the point where the luminance difference (absolute value) first exceeds the threshold, i.e., the point where the luminance difference (absolute value) first exceeds the threshold, is detected as the bead cutting end positions a and b, respectively. In all cases, the threshold level to be set can be the same as that of the conventional method.

[0034] As mentioned earlier, there are no particular restrictions on how the search start point is set within the bead cutting area; however, in the present invention, the seam position detection step is performed periodically at predetermined intervals along the longitudinal direction of the electric resistance welded steel pipe. Therefore, it is preferable to set the search start point within the bead cutting area specified by the bead cutting end positions a and b detected in the detection step immediately preceding the current detection step. In this case, the search start point can be set at any position within the bead cutting area specified by the bead cutting end positions a and b. As previously stated, if the interval between seam position detection steps (imaging interval) is not too long, the amount of variation in twist of the electric resistance welded steel pipe and the amount of variation in bead cutting width between detection steps are sufficiently small. For this reason, the bead cutting area specified by the bead cutting end positions a and b detected in the detection step immediately preceding the current detection step is considered to roughly coincide with the bead cutting area of ​​the current detection step.

[0035] Furthermore, it is particularly preferable to use the "seam position" (seam position S described later), which is identified by the bead cutting end positions a and b detected in the detection step immediately preceding the detection step, as the search starting point. This makes it possible to more reliably set the search starting point within the bead cutting area. In other words, as will be described later, in each detection step for the seam position, the center (midpoint) between the detected bead cutting end positions a and b can be set as the "seam position." Therefore, the "seam position" identified by the bead cutting end positions a and b detected in the detection step immediately preceding the detection step is considered to be within the bead cutting area of ​​that detection step with a fairly high probability.

[0036] In order to minimize the amount of twisting of the electric resistance welded steel pipe 10 and the amount of variation in bead cutting width between detection steps for seam detection, it is desirable to minimize the interval between detection steps for seam detection, i.e., the imaging interval, and specifically, it is preferable to have a pitch of 500 mm or less in the longitudinal direction of the steel pipe. However, in lines where the amount of twisting of the electric resistance welded steel pipe 10 and the amount of variation in bead cutting width are very small due to the equipment specifications of the manufacturing line, the imaging interval can be set to a longer pitch than the above 500 mm pitch. This makes it possible to reduce the specifications of the imaging device 1 and the image processing device 2, and to make a more inexpensive equipment configuration.

[0037] Even if the search start point in each detection step of seam detection is set within the area of ​​the bead cutting section as described above, it is necessary to set the initial position of the search start point in the first detection step of seam detection. This initial position of the search start point can be set by, for example, (i) referring to a table of initial values ​​for the search start point that has been set in advance according to the size and manufacturing conditions of the electric resistance welded steel pipe, or (ii) having the operator identify the position of the bead cutting section using a monitoring screen or the like and input the initial value of the search start point.

[0038] The seam position of the electric resistance welded steel pipe is determined based on the bead cutting end positions a and b. Specifically, the seam position coordinate X can be calculated by setting the midpoint between the bead cutting end positions a and b to the center (midpoint). However, if the offset amount between the seam position and the bead cutting position is predetermined based on the equipment positioning relationship of the electric resistance welded steel pipe manufacturing line or the detection technology described in Patent Document 2, the seam position S may be calculated from the bead cutting end position and the offset amount. The detection of the bead excavation end positions a and b, as described above, and the identification (calculation) of the seam position S based on these are performed as functions of the detection unit 4 of the image processing device 2. The seam position S and bead cutting end positions a and b are stored in the storage unit 5 of the image processing device 2 and can be referenced when setting the search start point when detecting the bead cutting end position in the next detection step.

[0039] As described above, according to the seam position detection method and apparatus of the present invention, even if the seam position shifts in the circumferential direction of the steel pipe due to twisting or pass line fluctuations of the electric resistance welded steel pipe 10 during manufacturing in the electric resistance welded steel pipe manufacturing line, the seam position S can be detected and identified with high accuracy along the entire length of the electric resistance welded steel pipe 10 without being affected by roll marks or black scale patterns on the steel pipe base material. Therefore, by transmitting information about the seam position S to the weld seam tracking device that determines the position of the annealer heater in the seam heat treatment equipment, it becomes possible to accurately position the annealer heater in the seam heat treatment equipment to the predetermined position. As a result, not only is the position correction work that was conventionally performed by operators reduced, but significant effects such as improved quality due to increased seam heat treatment speed and reduced power input can be obtained. Therefore, according to the present invention, high-quality electric resistance welded steel pipes can be manufactured. The details of the manufacturing method are as described above. [Examples]

[0040] As shown in Figure 1, a light source 3 that irradiates light onto the vicinity of the seam of the electric resistance welded steel pipe (the region including the seam and the bead cutting area), and an imaging device 1 that images the vicinity of the seam were installed downstream of the welding bead cutting machine 12 in the electric resistance welded steel pipe manufacturing line. The entire length of the electric resistance welded steel pipe was imaged using this imaging device 1 under diffuse reflection conditions, and the positions of the bead cutting area and the seam area were detected using the present invention method (example of the present invention) and the conventional method (conventional example) using the resulting brightness image, and the detection accuracy of the seam area was compared. The electric resistance welded steel pipe used had an outer diameter of 500 mm, and its entire length (160 m) was imaged at an imaging interval of 400 mm pitch, and the seam position was detected periodically at this interval.

[0041] In the present invention, in each detection step for the seam position, the "seam position" identified by the bead cutting end position detected in the previous detection step is set as the search starting point. A search is then performed from this search starting point toward both sides in the circumferential direction of the pipe, and the point where the brightness difference first exceeds the threshold (the point where the threshold is exceeded) is detected as the bead cutting end position. The midpoint between the detected bead cutting end positions is then defined as the "seam position". On the other hand, in the conventional method, the edge position of the brightness image was used as the starting point for searching for brightness differences, and the point where the brightness difference exceeded a threshold (a point above the threshold) was detected as the bead cutting edge position. The midpoint between the detected bead cutting edge positions was then defined as the "seam position."

[0042] The detection accuracy was evaluated by determining that detection was good if the difference between the seam position detected by the present invention method and the conventional method and the true seam position identified visually from the captured image was 1.0 mm or less. As a result of the evaluation, even in captured images like Figure 5, which resulted in false detection with the conventional method, detection was good with the present invention method. Furthermore, while detection accuracy was good in 87.9% of the area with the conventional method over the entire length of the electric resistance welded steel pipe, detection accuracy was good in 98.1% of the area with the present invention method, demonstrating a significant improvement in seam detection accuracy over the entire length of the electric resistance welded steel pipe. [Explanation of symbols]

[0043] 1. Imaging device 2 Image Processing Device 3 light source 4. Detection Unit 5 Storage section 10 ERW steel pipe 11 Squeeze Roll 12 Weld bead cutting machine 13. Seam heat treatment equipment a,b Bead cutting end position S Seam position

Claims

1. A method for detecting the seam portion of an electric resistance welded steel pipe in a manufacturing line for electric resistance welded steel pipes, Step (A) involves imaging the area near the seam where light is irradiated from a light source, downstream of the cutting position of the weld bead. Step (B) involves detecting the positions of both ends of the bead cutting portion from the brightness image of the seam area captured in step (A), The process includes a step (C) to identify the seam position based on the positions of both ends of the bead cutting portion detected in step (B), A method for detecting the seam position of an electric resistance welded steel pipe, characterized in that, in step (B) above, the starting point for searching for the end position of the bead cutting portion with respect to the brightness image is set within the area of ​​the bead cutting portion, the search is performed from the starting point toward both sides in the circumferential direction of the pipe, and the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe) first exceeds a threshold is detected as the end position of the bead cutting portion.

2. Along the longitudinal direction of the electric resistance welded steel pipe, the seam position detection steps (A) to (C) described above are performed periodically at predetermined intervals. The method for detecting the seam position of an electric resistance welded steel pipe according to claim 1, characterized in that in step (B), a search start point is set within the region of the bead cutting portion identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step.

3. Along the longitudinal direction of the electric resistance welded steel pipe, the seam position detection steps (A) to (C) described above are performed periodically at predetermined intervals. The method for detecting the seam position of an electric resistance welded steel pipe according to claim 1, characterized in that in step (B), the seam position identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step is set as the starting point for the search.

4. The method for detecting the seam position of an electric resistance welded steel pipe according to any one of claims 1 to 3, characterized in that in step (C), the center between the positions of both ends of the detected bead cutting portion is identified as the seam portion position.

5. A method for manufacturing electric resistance welded steel pipes in an electric resistance welded steel pipe manufacturing line, while detecting the seam portion of the electric resistance welded steel pipe, Step (A) involves imaging the area near the seam where light is irradiated from a light source, downstream of the cutting position of the weld bead. Step (B) involves detecting the positions of both ends of the bead cutting portion from the brightness image of the seam area captured in step (A), The process includes a step (C) to identify the seam position based on the positions of both ends of the bead cutting portion detected in step (B), A method for manufacturing electric resistance welded steel pipes, characterized in that, in step (B) above, the starting point for searching for the end position of the bead cutting portion with respect to the brightness image is set within the area of ​​the bead cutting portion, the search is performed from the starting point toward both sides in the circumferential direction of the pipe, and the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe) first exceeds a threshold is detected as the end position of the bead cutting portion.

6. Along the longitudinal direction of the electric resistance welded steel pipe, the seam position detection steps (A) to (C) described above are performed periodically at predetermined intervals. The method for manufacturing an electric resistance welded steel pipe according to claim 5, characterized in that in step (B), a search start point is set within the region of the bead cutting portion identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step.

7. Along the longitudinal direction of the electric resistance welded steel pipe, the seam position detection steps (A) to (C) described above are performed periodically at predetermined intervals. The method for manufacturing an electric resistance welded steel pipe according to claim 5, characterized in that in step (B), the seam position identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step is set as the starting point for the search.

8. The method for manufacturing electric resistance welded steel pipes according to any one of 5 to 7, characterized in that, in step (C), the center between the positions of both ends of the detected bead cutting portion is identified as the seam portion position.

9. A device for detecting the seam portion of electric resistance welded steel pipes in a manufacturing line for electric resistance welded steel pipes, An imaging device (1) captures images of the area near the seam where light is irradiated from a light source, downstream of the cutting position of the weld bead, The imaging device (1) captures a brightness image of the vicinity of the seam, and the image processing device (2) detects the positions of both ends of the bead cutting portion from this image and identifies the position of the seam based on the detected positions of both ends of the bead cutting portion. The image processing device (2) is characterized by setting a search starting point within the area of ​​the bead cutting portion when searching for the end position of the bead cutting portion with respect to the brightness image, performing a search from the search starting point toward both sides in the circumferential direction of the pipe, and detecting the point where the brightness or brightness difference (however, the brightness difference between adjacent cells in the circumferential direction of the pipe) first exceeds a threshold as the end position of the bead cutting portion.

10. A seam position detection device that periodically performs a seam position detection step along the longitudinal direction of an electric resistance welded steel pipe at predetermined intervals, wherein the imaging device (1) images the vicinity of the seam, and the image processing device (2) detects the position of the seam based on the brightness image obtained from the imaging, The image processing device (2) stores the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step, and sets a search start point within the area of ​​the bead cutting portion identified by the positions of both ends of the bead cutting portion, as described in claim 9, for detecting the seam position of an electric resistance welded steel pipe.

11. A seam position detection device that periodically performs a seam position detection step along the longitudinal direction of an electric resistance welded steel pipe at predetermined intervals, wherein the imaging device (1) images the vicinity of the seam, and the image processing device (2) detects the position of the seam based on the brightness image obtained from the imaging, The image processing device (2) stores the seam position identified by the positions of both ends of the bead cutting portion detected in the detection step immediately preceding the detection step, and sets the seam position as the starting point for the search, as described in claim 9.

12. The image processing device (2) is characterized in that it identifies the center between the positions of both ends of the detected bead cutting portion as the seam portion position, as described in any one of 9 to 11, for the seam position detection device for electric resistance welded steel pipes.

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